Shellenberger Thomas D, Wang Mary, Gujrati Manu, Jayakumar Arumugam, Strieter Robert M, Burdick Marie D, Ioannides Constantin G, Efferson Clayton L, El-Naggar Adel K, Roberts Dianna, Clayman Gary L, Frederick Mitchell J
Department of Head and Neck Surgery, University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030, USA.
Cancer Res. 2004 Nov 15;64(22):8262-70. doi: 10.1158/0008-5472.CAN-04-2056.
BRAK/CXCL14 is a CXC chemokine constitutively expressed at the mRNA level in certain normal tissues but absent from many established tumor cell lines and human cancers. Although multiple investigators cloned BRAK, little is known regarding the physiologic function of BRAK or the reason for decreased expression in cancer. To understand the possible significance associated with loss of BRAK mRNA in tumors, we examined the pattern of BRAK protein expression in normal and tumor specimens from patients with squamous cell carcinoma (SCC) of the tongue and used recombinant BRAK (rBRAK) to investigate potential biological functions. Using a peptide-specific antiserum, abundant expression of BRAK protein was found in suprabasal layers of normal tongue mucosa but consistently was absent in tongue SCC. Consistent with previous in situ mRNA studies, BRAK protein also was expressed strongly by stromal cells adjacent to tumors. In the rat corneal micropocket assay, BRAK was a potent inhibitor of in vivo angiogenesis stimulated by multiple angiogenic factors, including interleukin 8, basic fibroblast growth factor, and vascular endothelial growth factor. In vitro, rBRAK blocked endothelial cell chemotaxis at concentrations as low as 1 nmol/L, suggesting this was a major mechanism for angiogenesis inhibition. Although only low affinity receptors for BRAK could be found on endothelial cells, human immature monocyte-derived dendritic cells (iDCs) bound rBRAK with high affinity (i.e., K(d), approximately 2 nmol/L). Furthermore, rBRAK was chemotactic for iDCs at concentrations ranging from 1 to 10 nmol/L. Our findings support a hypothesis that loss of BRAK expression from tumors may facilitate neovascularization and possibly contributes to immunologic escape.
BRAK/CXCL14是一种CXC趋化因子，在某些正常组织中以mRNA水平组成性表达，但在许多已建立的肿瘤细胞系和人类癌症中不存在。尽管有多位研究者克隆了BRAK，但关于BRAK的生理功能或其在癌症中表达降低的原因知之甚少。为了了解肿瘤中BRAK mRNA缺失可能具有的意义，我们检测了舌鳞状细胞癌（SCC）患者正常和肿瘤标本中BRAK蛋白的表达模式，并使用重组BRAK（rBRAK）来研究其潜在的生物学功能。使用肽特异性抗血清，在正常舌黏膜的基底层以上发现BRAK蛋白大量表达，但在舌SCC中始终不存在。与先前的原位mRNA研究一致，BRAK蛋白在肿瘤邻近的基质细胞中也强烈表达。在大鼠角膜微袋试验中，BRAK是多种血管生成因子（包括白细胞介素8、碱性成纤维细胞生长因子和血管内皮生长因子）刺激的体内血管生成的有效抑制剂。在体外，rBRAK在低至1 nmol/L的浓度下就能阻断内皮细胞趋化，表明这是血管生成抑制的主要机制。尽管在内皮细胞上仅能发现BRAK的低亲和力受体，但人未成熟单核细胞衍生的树突状细胞（iDCs）能以高亲和力（即解离常数K(d)约为2 nmol/L）结合rBRAK。此外，rBRAK在1至10 nmol/L的浓度范围内对iDCs具有趋化作用。我们的研究结果支持这样一种假说，即肿瘤中BRAK表达的缺失可能促进新血管形成，并可能导致免疫逃逸。
